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DATA FLOW DIAGRAMS
UNIT 6: DATA FLOW DIAGRAMS
Creating Data Flow Diagrams
 Introduction
 Data Flow Diagrams (DFD)
 Reading Data Flow Diagrams
 Elements of Data Flow
Diagrams
 Using DFD to Define Business
Process
 Process Descriptions
 Creating Data Flow Diagrams
 Context Diagram
 Level 0 Diagram
 Level 1 Diagram (and Below)
 Validating Data Flow Diagrams
CREATING DATA FLOW DIAGRAMS
 Process model describes business process-the activities that people
do. Process models are developed for the as-is system and/or the tobe system.
 Data flow diagramming, one of the most commonly used process
modeling techniques.
INTRODUCTION
Process model
 A formal way of representing how a business system operates.
 Illustrates/Explain the activities that are performed and how data moves among them.
Data flow diagramming
 A common technique for creating process models
INTRODUCTION
 Logical process models describe processes without suggesting how
they are conducted
 Physical process models provide information that is needed to build
the system
ELEMENTS OF DFD
ELEMENTS OF DFD
USING DFD TO DEFINE BUSINESS PROCESS
 Business processes are too complex to be shown on a single DFD.
 Decomposition is the process of representing the system in a
hierarchy of DFD diagrams.
 Child diagrams show a portion of the parent diagram in greater
detail.
 Balancing involves insuring that information presented at one level of
a DFD is accurately represented in the next level DFD.
USING DFD TO DEFINE BUSINESS PROCESS
PROCESS DESCRIPTIONS
 Text-based process descriptions provide more information about the
process than the DFD alone.
 If the logic underlying the process is quite complex, more detail may
be needed in the form of
Structured English
Decision trees
Decision tables
CREATING DATA FLOW DIAGRAMS
CONTEXT DIAGRAMS
 The first DFD in every business process model.
 Context Diagram shows the entire system as context with it's
environment.
 All process models have only one context diagram.
 Context diagram shows overall process as just one process.
 Context Diagram shows data flows with external entities or/and any
other systems in the organization.
CONTEXT DIAGRAMS
CONTEXT DIAGRAMS
 In a Patient Information system in a hospital, the system will interact
with three entities (Patient, Insurance company, and doctors).
CONTEXT DIAGRAMS
 There are many data exchanging between the system and the
patient, such as:
Collect patient information (i.e. name, phone and address …).
Receive an appointment request from the patient.
Receive payment information from the patient
Deliver appointments schedule to the patient
Deliver bills details to the patients
CONTEXT DIAGRAMS
 And there are only two data flows with Insurance company:
Sending bills to the company
And receiving Payment information
CONTEXT DIAGRAMS
 And finally the system will produce the following reports to doctors:
Appointment report
Patient report
Financial reports
QUESTION
 Draw the context diagram for student information system
LEVEL 0 DIAGRAM
 Once you have the set of DFD fragments (One for each use case) you
simply combine them into one DFD drawing that becomes Level 0
DFD.
 In this DFD you'll add data stores.
 Level 0 diagrams show the major process within the system, and
major process within external entities, which are the sources or
destination of data flows.
LEVEL 0 DIAGRAM
 Try to put the first chronologically process to the left top corner, and
then draw the diagram bottom right ways.
 Reduce the number of crosses as few as possible.
 Iteration is the cornerstone of good DFD design, the first time draw
DFD to understand the system.
 Second iteration; draw it for better understanding and to reduce
number of crosses. And so on.
LEVEL 0 DIAGRAM
 On Doctors office system, we have four different use cases in level 1,
make appointment, maintain patient info, perform billing, and
prepare management reports.
 So you ( as analysts) have a choice to draw them all in one diagram
(witch is preferred) or to divide them into four different diagrams.
 The following is a cut of the level 0 diagram
LEVEL 0 DIAGRAM PROCESS 1
LEVEL 0 DIAGRAM PROCESS 2
LEVEL 0 DIAGRAM PROCESS 3
LEVEL 0 DIAGRAM PROCESS 4
LEVEL 0 DIAGRAM “EXPLAIN”
 Patient provides his/here information (Name, and Address).
 Process 1 checks patient's state in Patients Data Store, to update or
insert …
 Patient requests an appointment in a suitable time for him/her.
 The process checks availability of these times by querying
Appointments Data Store.
LEVEL 0 DIAGRAM “EXPLAIN”
 Then Process 1 provides the patient with a potential appointments
 So the patient will select the most suitable appointment.
 And the Process finally updates Appointments Data Store to assign
the selected appointment.
 And finally informs the patient with this/here selection to be
confirmed.
LEVEL 1 DIAGRAM
 Generally, one level 1 diagram is created for every major process on
the level 0 diagram.
 Shows all the internal processes that comprise a single process on
the level 0 diagram.
 The process for creating the level 1 DFDs is to take the steps as
written on the use cases and convert them into a DFD in much the
same way as for the level 0.
LEVEL 1 DIAGRAM
 Shows how information moves from and to each of these processes
 If a parent process is decomposed into, for example, three child
processes, these three child processes wholly and completely make
up the parent process
Level 1 Diagram Example
Reading Data Flow Diagrams
TO EXPLAIN THE CHART
 This chart for a doctor office.
 People start reading the diagrams from top-left corner of the DFD.
 The item "Patient" is an external entity.
 "Patient" entity has four different arrows pointing away from itself,
represent bundles of data.
TO EXPLAIN THE CHART
 Rounded rectangles such as "Get Patient Name and Address" are
actions/process that are performed.
 Arrows are data flows, an arrow that pointing to an entity, or pointing
to a process represent the inputs for this entity or process.
 Arrows that pointing out of the entity/process represent outputs for
this entity/process.
VALIDATING DATA FLOW DIAGRAMS
VALIDATING DATA FLOW DIAGRAMS
 There are two fundamentally different types of problems that can
occur in DFDs, syntax errors and semantic errors.
 Syntax Errors: refers to structure of the DFDs and whether the DFDs
follow the rules of the language.
 Semantic Errors: refers to the meaning of the DFDs and whether they
accurately describe the business process being modeled.
FOR EACH DFD:
 Check each data flow for:
 A unique name: noun; description
 Connects to at least one process
 Shown in only one direction (no two-headed arrows)
 A minimum number of crossed lines
FOR EACH DFD:
 Check each data store for:
A unique name: noun; description
At least one input data flow
At least one output data flow
FOR EACH DFD:
 Check each external entity for:
 A unique name: noun; description
 At least one input or output data flow
ACROSS DFDS:
Context Diagram:
 Every set of DFDs must have one Context Diagram
Viewpoint:
 There is a consistent viewpoint for the entire set of DFDs
ACROSS DFDS:
Decomposition:
 Every process is wholly and complete described by the processes on
its children DFDs
Balance:
 Every data flow, data store, and external entity on a higher level DFD
is shown on the lower level DFD that decomposes it No data stores or
data flows appear on lower-lever DFDs that do not appear on their
parent DFD.
SUMMARIZE THE LECTURE
 DFD
 DFD Elements
 DFD Levels
Context Diagram
Level 0
Level 1
Level 2
 Validating DFD

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